The U.S. Senate has passed a bill, introduced by Michigan Senator Debbie Stabenow, that prohibits gag clauses on pharmacists.

Stabenow says insurance co-pays are sometimes more than the out-of-pocket price of a prescription drug.

But the companies that manage drug benefits often put a gag clause in their contracts with pharmacies. So pharmacists can't tell their customers there's a cheaper way to get the drug.

Her bill, if signed by the President, would ban such clauses in Medicare Part D contracts.

"So that pharmacists have the freedom to tell their customers the best way to get the lowest price at the counter, and it seems pretty basic to me," says Stabenow.

Stabenow says a recent study shows the gag clauses are increasing costs for patients. The study found nearly 25% of patients paid more than necessary for prescription drugs.

Michigan Pharmacists Association CEO Larry Wagenknecht says cost is often a factor in whether patients adhere to their treatment plans. If people can't afford their prescriptions, they might not fill them, or they might cut pills in half when they shouldn't.

A similar bill moving through the House would ban the gag clauses for private drug benefit plans.